Rigid motorcycle frames offer simplicity in design, classic lines, a clean look, and ample space for placement of other motorcycle components. However, rigid frames provide relatively little shock dampening and a resulting rough ride. An example of a rigid frame is sketched in FIGS. 5A, 5B and 5C, which shows tubular frame members comprising left and right wishbone members 61a and 61b that connected to axle plates 62a and 62b and converged together on the centerline of the frame, at about mid-frame forward in FIG. 5C. Steering neck 63 is at the front of the frame.
Softail® style and “swing arm” style frames are two popular frame styles that provide suspension systems for a smoother, more comfortable ride. Softail® style frames, an example of which is partially sketched in FIG. 7, has a rear frame 90 that is pivotally mounted to the main frame 91 and one or two shock absorbers 86 mounted between the main frame and rear frame a distance away from the pivot axis, which axis runs through pivot connection features 85a, 85b, 87a and 87b. The shock absorbers stabilize the rear frame while allowing a range of rotational motion about the pivot axis under changing load conditions, and they attenuate shock loads imparted on the rear frame. They also attenuate the transfer of shock load from the rear frame to the main frame.
The swing arm frame is another popular frame design, an example of which is roughly illustrated in FIGS. 6A and 6B, has a swing arm (with two forks 74a and 74b) pivotally mounted at pivot point 75 to the main frame and one or more shock absorbers 76a and 76b mounted between the arm and the main frame.
Softail® style and swing-arm style suspension systems are less attractive than rigid frames, occupy substantially more space in the frame compartment, and require significant maintenance. The rear pivot connection may have bearings which can wear out and require replacement, and the shock absorbers also require maintenance over time. These suspension systems, like in virtually every motorcycle rear-wheel suspension system are pivoting systems. Pivoting systems may restrain component movement to an arc shaped path, and are less effective at attenuating shock loads directed radially through the center of the pivot axis.
There is a need for a pivotless motorcycle suspension system. The terms “pivotless”, “pivotless connection”, “pivotless joint”, and “pivotless suspension” hereinafter should be interpreted in the context of the foregoing background as referring to connections, joints or systems that are without structure creating a joint between two parts that allows the parts to move relative to one another in a swiveling (or “swinging”) motion about the joint during operation of a motorcycle. There is a need for a motorcycle frame that provides classic lines, a clean look, and ample space for placement of other components like a rigid frame, while at the same time providing a suspension system for a smoother and more comfortable ride. There is a need for a suspension system that distributes force over four absorbers, provides more freedom of motion than an arc of a pivoting system, eliminates rigid shock dynamics in the radial direction through a pivot point, and simplifies maintenance.
The present invention fills those and other needs with an efficient design that requires few parts and low maintenance.